Optical multiple transmission method, optical network and optical transmission apparatus

ABSTRACT

In a known wavelength multiplexer, optical signals to pass are passed with their wavelengths held identical. Therefore, unless an unused wavelength common to all zones exists in case of setting an optical channel, the channel cannot be set. According to the present invention, a drop/add type wavelength multiplexer includes a wavelength converting section ( 50  in FIG.  5 ) which converts the wavelengths of optical signals to pass from the input side of the multiplexer to the output side thereof. In a network employing the wavelength multiplexers at individual nodes, a new optical channel can be easily set by utilizing wavelengths not used at the nodes.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a wavelength multiplexingtransmission method and an optical network in which a plurality ofoptical signals of different wavelengths are multiplexed andtransmitted, and an optical transmission apparatus which can be used forthe transmission method and the optical network.

[0002] Heretofore, a method as stated below has been known as anexpedient for extending a ring network based on wavelength multiplexingtechnology. It is contained in, for example, Rajiv Ramanswasmi and KumarN. Sivarajan: “Optical Networks—A Practical Perspective—” published byMorgan Kaufmann Publishers, page 449. A general construction for themethod has been as shown in, for example, FIG. 10. 15 in the book. Themethod is founded on the construction that, in case of realizing a ringnetwork of the type which drops or adds only specific wavelengths,optical signals of wavelengths propagating via a certain node apparatusare outputted at the same wavelengths as the inputted wavelengths.Accordingly, a practicable node apparatus is constructed including adropping section in which any signals are derived from a wavelengthdemultiplexing unit located on the input side of the node apparatus andare outputted outside, and an adding section in which optical signalsgiven from outside are connected to a wavelength multiplexing unitlocated on the output side of the node apparatus. Herein, the certainwavelength signals delivered from the wavelength demultiplexing unit aredirectly delivered to the wavelength multiplexing unit as the signalshaving the same wavelengths. Thus, the optical signals which are droppedor added by the apparatus itself are externally outputted or inputtedvia the dropping section or the adding section. On this occasion, theapparatus does not drop or add any wavelengths for itself, but ittransmits the optical signals inputted for other apparatuses, from oneside to the other side thereof without changing the wavelengths of theoptical signals. Although the network of ring scheme (ring network) isexemplified here, a similar method is known also in a linear network.The “linear network” is a network architecture wherein node apparatusesare arrayed in one row, and wherein optical signals of any wavelengthsare dropped or added by the node apparatuses arranged midway.

[0003] Next, a node apparatus for such a network will be concretelyexemplified. FIG. 1 shows an example of the node apparatus which has awavelength multiplexing function and which incarnates the dropping andadding of specific wavelengths. A wavelength dropping section includes afirst space switching unit 1, a wavelength demultiplexing unit 3 and aninterface unit 5 for input wavelength-multiplexed optical signal 7. Thewavelength demultiplexing unit 3 demultiplexes the inputwavelength-multiplexed optical signal 7 into individual wavelengths (λ1,λ2, λ3, . . . , λN), which are respectively delivered to predeterminedtransmission lines 9. The first space switching unit 1 drops opticalsignal of desired specific wavelengths in the inputwavelength-multiplexed optical signal 7. The interface unit 5 outputsthe dropped input lights as desired dropped optical signals. Thus, thewavelength dropping section demultiplexes the inputwavelength-multiplexed optical signal 7 into the individual wavelengthsand drops the desired wavelengths so as to output the dropped opticalsignals 12.

[0004] On the other hand, a wavelength adding section includes aninterface unit 6, a second space switching unit 2 and a wavelengthmultiplexing unit 4 for output wavelength-multiplexed optical signal 8.The interface unit 6 outputs optical signals to-be-added 13. Opticalsignals 10 transmitted from the first space switching unit 1, and theoptical signals to be-added 13 transmitted from the interface unit 6 aredelivered to predetermined transmission lines 11 via the second spaceswitching unit 2 in accordance with connection route settings for theoptical signals respectively having the individual wavelengths. Theoptical signals 11 of the plurality of wavelengths (λ1, λ2, λ3, . . . ,λN) thus delivered are wavelength-multiplexed by the output wavelengthmultiplexing unit 4, and the resulting optical signal is outputted asthe wavelength-multiplexed optical signal 8. Here, each of the firstspace switching unit 1 and the second space-switching unit 2 isconstructed of optical switches etc.

[0005] Apart from the above expedient in which the dropping or addingsection is constructed of the optical switches, a wavelength multiplexerof drop/add type employing “Fiber Bragg Grating” technology has alsobeen proposed. The drop/add type wavelength multiplexer is illustratedin, for example, FIG. 3. 60 on page 172 of the aforementioned book“Optical Networks—A Practical Perspective—”. The fiber Bragg gratingtechnology is optical filter technology which utilizes periodicalrefractive index modulation within an optical fiber as is formed whenthe optical fiber doped with Ge (germanium) is irradiated with theinterference fringes of ultraviolet light. The construction of thedrop/add type wavelength multiplexer employing the fiber Bragg gratingtechnology is shown in FIG. 2. A light dropping section 20 includes acirculator 26 and a splitter 27. In the circulator 26, light propagatingrightwards from left is totally transmitted, whereas light propagatingleftwards from right is totally reflected downward to the splitter 27 asviewed in the figure. In fiber Bragg gratings 24, only lights ofwavelengths λ1, λ2, λ3 and λ4 in the rightward light are totallyreflected leftwards. A light adding section 22 includes a combiner 28and a coupler 29. In the figure, numeral 7 indicates the inputwavelength-multiplexed optical signal, and numeral 8 indicates theoutput wavelength-multiplexed optical signal.

[0006] With the fiber Bragg grating technology, the optical signals ofthe specific wavelengths are derived by a diffraction grating at aninput stage in a state where the wavelengths are multiplexed as theyare.

[0007] It is common to both the dropping/adding methods stated abovethat the wavelengths of optical signals which are transmitted remainunchanged.

[0008] A network wherein a plurality of node apparatuses of the typedropping and adding optical signals of specific wavelengths areconnected, has a difficulty as explained below.

[0009] In the network wherein the plurality of apparatuses dropping andadding the optical signals of specific wavelengths are connected in aring scheme or a linear scheme, a request for connecting an opticalchannel is generally made by designating any two of the plurality ofapparatuses which constitute the whole network. In that case, regardingwhich of wavelengths is to be used for the connection, a wavelength notused in any zone is selected in accordance with the situation of uses ofthe wavelengths in all zones. Various algorithms corresponding to theindividual aspects of uses have been proposed for the selection. Typicalexamples of the algorithms are as follows, The first example is a methodwherein fixed Nos. denoted by natural numbers are assigned towavelengths usually applied, and wherein an unused wavelength isselected from the smaller one of the Nos. The second example is a methodwherein any wavelength is selected from among unused wavelengths byemploying a random number.

[0010] In an actual transmission circuit, however, a problem is posed asstated below. In general requests for channels to be connected are notfully determined at the time of the construction of the network.Accordingly, the optical channels of the transmission circuit are addedor deleted in accordance with the requests for channels arising everyday, and the settings of the channels need to be altered incorrespondence with the addition or deletion of the optical channels.

[0011] With the prior-art technique mentioned above, it is required toselect the wavelength which is not used in any of all the zones of thechannel. Accordingly, when a request for connection has occurred in acertain channel, a wavelength which is not used in any of the zonesincluded from a certain apparatus to another apparatus must be selected.In the nonexistence of such a wavelength, the optical transmissionchannel requested to be connected cannot be connected in spite of theexistence of unused wavelengths in the individual zones.

[0012] This state is shown in FIG. 3. The figure exemplifies an opticalnetwork in the case where node apparatuses A-E, i.e. five apparatuses100, 101, 102, 103 and 104 are connected in one row. Letters a, b, c, .. . and h indicate channels which are respectively connected to the nodeapparatuses. The respectively adjacent apparatuses are connected by amultiplex channel of four wavelengths. That is, the multiplex channelcan accommodate, up to, four optical channels. Incidentally, the case ofthe four wavelengths is mentioned here, but in general, the number ofwavelengths is not especially restricted. Besides, although the nodeapparatuses are connected in one row in the example of FIG. 3, the sameholds true even when node apparatuses are connected in a ring shape orin a mesh shape. Further, the algorithm of minimum value selection as isthe simplest algorithm shall be adopted here. Also, a request for achannel shall be an additional request in the ensuing description.

[0013] It is now assumed that requests for connections have occurred inthe order of the channels a, b, c, d, . . . and g. Then, the wavelengthsof the smallest Nos. usable in compliance with the requests for theconnections of the channels are selected on the basis of the algorithmof the minimum value selection. Thus, the seven channels from thechannel a to the channel g are set as shown in FIG. 3. By way ofexample, the channel a connects the node apparatuses A and B, and thewavelength of wavelength No. 1 is used for the channel. The connectionsof the other channels are similarly understood. Here, it must beattended to that, in the case of the method which uses the samewavelengths in all the channels connected, each of the node apparatusesoutputs the same wavelengths as the inputted wavelengths.

[0014] It is now considered that the request for the connection of thechannel h has been further added. The channel h corresponds to therequest for the connection from the node apparatus B to the nodeapparatus E. When the situation of uses of the wavelengths in the nodeapparatus C is viewed here, wavelength Nos. 3 and 4 are already used onthe left side (on the side of the node apparatus B), and wavelength Nos.1 and 2 are already used on the right side (on the side of the nodeapparatus E). Consequently, any wavelength usable on both the right andleft sides in common does not exist in the node apparatus C.Accordingly, this example involves the problem that the channel h cannotbe added though the node apparatus although C has the unused wavelengthson both the right and left sides. For adding the channel h, therefore,it is necessary to build, for example, another network of ring schemeconstituted by a plurality of similar apparatuses. This means that awavelength multiplexing capability is not fully exploited in themultiplex system of wavelength multiplexing.

SUMMARY OF THE INVENTION

[0015] The main aspects of the present invention are as follows:

[0016] In accordance with a first aspect of the present invention, thereis provided an optical multiplex transmission method comprisingaccepting an optical signal group in which optical signals of aplurality of wavelengths are multiplexed, from a first opticaltransmission line; converting the optical signal of the first wavelengthincluded in the optical signal group, into the optical signal of thesecond wavelength different from said first wavelength; and multiplexingat least one of the optical signals of the wavelengths except said firstwavelength, included in said optical signal group, and said opticalsignal of said second wavelength, and then outputting the resultingmultiplexed optical signals to a second transmission line.

[0017] In accordance with a second aspect, there is provided an opticalmultiplex transmission method comprising accepting a first opticalsignal group in which optical signals of a plurality of wavelengths aremultiplexed, from a first optical transmission line, and a secondoptical signal group in which optical signals of a plurality ofwavelengths are multiplexed, from a second optical transmission line;converting the optical signal of the first wavelength included in thefirst optical signal group, into the optical signal of the secondwavelength different from said first wavelength; multiplexing at leastone of the optical signals included in said first optical signal group,at least one of the optical signals included in the second opticalsignal group, and said optical signal of said second wavelength, andthen outputting the resulting multiplexed optical signals to a thirdoptical signal line; and multiplexing at least one of the opticalsignals except the optical signals to be outputted to the third opticalsignal line, included in said first optical signal group, and at leastone of the optical signals except said optical signals to be outputtedto said third optical signal line, included in said second opticalsignal group, and then outputting the resulting multiplexed opticalsignals to a fourth optical signal line.

[0018] In accordance with a third aspect, there is provided an opticalmultiplex transmission method comprising allowing a first node apparatusto receive a wavelength-multiplexed optical signal group; to transmit atleast one of optical signals included in the optical signal group, to asecond node apparatus connected with the first node apparatus; toconvert the optical signal of first wavelength included in said opticalsignal group, into the optical signal of second wavelength differentfrom the first wavelength; and to transmit said optical signal of thesecond wavelength to a third node apparatus connected with said firstnode apparatus.

[0019] In accordance with a fourth aspect, there is provided an opticaltransmission apparatus comprising an input wavelength demultiplexingunit which demultiplexes a first optical signal group including opticalsignals of a plurality of wavelengths inputted from a first opticalfiber, into the optical signals of the respective wavelengths; awavelength multiplexing unit which multiplexes optical signals of aplurality of wavelengths, and which outputs the resulting multiplexedoptical signals to a second optical fiber; a wavelength dropping unitwhich outputs predetermined optical signals among said optical signalsof said respective wavelengths demultiplexed by said input wavelengthdemultiplexing unit; a wavelength adding unit which outputspredetermined optical signals in a second optical signal group includingoptical signals of a plurality of wavelengths externally inputted, tosaid wavelength multiplexing unit; and a wavelength converting unitwhich converts the optical signal of first wavelength among said opticalsignals of said respective wavelengths demultiplexed by said inputwavelength demultiplexing unit, into the optical signal of secondwavelength different from the first wavelength, and which outputs saidoptical signal of the second wavelength to said wavelength adding unit.

[0020] Further aspects of the present invention will become apparentfrom the ensuing description.

[0021] The essentials of the present invention will be summed up below.The difficulty in the optical transmission described above is ascribableto the restriction of an apparatus construction that optical signals tobe passed through each apparatus of any optical network must haveidentical wavelengths on the input side and output side of theapparatus. Here, if an optical signal of certain wavelength from theinput side can be converted into an optical signal of differentwavelength within the apparatus so as to externally output the resultingoptical signal, and if any unused wavelengths are respectively existenton the input side and the output side, the unused wavelengths will bepermitted to pass through the apparatus irrespective of whether or notthese wavelengths are in agreement.

[0022] This fact holds true also of optical signals which are connectedvia a plurality of zones. If the apparatuses can convert the wavelengthsof the optical signals to be passed, and if unused wavelengths arerespectively existent in the plurality of zones desired to be connected,it is permitted to set a corresponding optical channel, irrespective ofthe combination of the unused wavelengths. According to such a method,the maximum number of wavelengths can be utilized between the zones, andthe capability of wavelength multiplexing can be exploited to theutmost.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a block diagram showing an example of construction of adrop/add type wavelength multiplexer in the prior art;

[0024]FIG. 2 is a diagram showing an example of construction of adrop/add type wavelength multiplexer which employs fiber Bragg gratingtechnology;

[0025]FIG. 3 is a diagram for explaining a prior-art method of settingwavelength routes in drop/add type wavelength multiplexing transmission;

[0026]FIG. 4 is a diagram for elucidating the principle of the presentinvention in the drop/add type wavelength multiplexing transmission;

[0027]FIG. 5 is a block diagram showing the construction of a drop/addtype wavelength multiplexer in an embodiment of the present invention;

[0028]FIG. 6 is a diagram showing an example in which a wavelengthconverting section in the embodiment is constructed of electricswitches;

[0029]FIG. 7 is a diagram showing an example in which the wavelengthconverting section in the embodiment is constructed of optical switches;

[0030]FIG. 8 is a block diagram showing the construction of a drop/addtype wavelength multiplexer in another embodiment of the presentinvention;

[0031]FIG. 9 is a diagram showing a linear network in an embodiment ofthe present invention;

[0032]FIG. 10 is a diagram showing a ring network in an embodiment ofthe present invention;

[0033]FIG. 11 is a diagram showing a meshed network in an embodiment ofthe present invention; and

[0034]FIG. 12 is a flow chart for explaining examples of operations inthe network in an embodiment of the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

[0035] The principle of the present invention will be elucidated withreference to FIG. 4. The figure is a conceptual diagram of an opticalnetwork for describing the basic idea of the present invention. Likewiseto FIG. 3, FIG. 4 exemplifies the optical network in the case where nodeapparatuses A-E, i.e. five apparatuses 110, 111, 112, 113 and 114 areconnected in one row. Letters a, b, c, . . . and h indicate channelswhich are respectively connected to the node apparatuses. Each nodeapparatus is exemplified as a multiplexer of four wavelengths, and itcan accommodate, up to, four optical channels. Incidentally, the case ofthe four wavelengths of wavelengths Nos. 1 through 4 is mentioned here,but in general, the number of wavelengths is not especially restrictedin the optical network to which the present invention is directed.Besides, although the node apparatuses are connected in one row in theexample of FIG. 4, the present invention is similarly applicable to adifferent connection scheme. The different connection scheme correspondsto, for example, a case where node apparatuses are connected in a ringshape or in a mesh shape.

[0036] The example as shown in FIG. 3 has the fundamental rule that thewavelengths propagating via the node apparatuses are the same. Asexplained before, under such a rule, there is the problem that anychannel cannot be increased in spite of the existence of unusedwavelengths in individual zones.

[0037] In contrast, according to the present invention, the abovedifficulty is avoided in such a way that each node apparatus convertsthe wavelength of the inputted light so as to output the resultingwavelength. Referring to FIG. 4, in a case where a request forconnecting the channel h between the node apparatuses B and E has beenreceived, the node apparatus C located midway executes the wavelengthconversion. Owing to the wavelength conversion, the signal of wavelengthNo. 1 is converted into that of wavelength No. 3. It is consequentlypermitted to set the channel h anew. The function of this wavelengthconversion is indicated as “Wavelength conversion 1” in the figure.Besides, in a case where a request for connecting a channel i betweenthe node apparatuses B and D has been further received here, the nodeapparatus C similarly executes the wavelength conversion from wavelengthNo. 2 into wavelength No. 4. Thus, the channel i is set. The function ofthis wavelength conversion is indicated as “Wavelength conversion 2” inthe figure.

[0038] Now, practicable embodiments of the node apparatus itselfaccording to the present invention will be described.

[0039] In general, the node apparatus is capable of two-waytransmissions. In each of the ensuing embodiments, however, only theconstruction of the transmission in one way will be shown for thebrevity of illustration. In order to realize the two-way transmissions,the node apparatus may include besides the construction of eachembodiment, the same construction so as to reverse a transmittingdirection. Further, two examples stated below are representative as awavelength multiplexing method. The first is a one-way wavelengthmultiplexing system wherein wavelengths for one way are multiplexed in asingle optical fiber. The second is a two-way wavelength multiplexingsystem wherein wavelengths for two ways are multiplexed in a singleoptical fiber. In the present invention, how to construct the nodeapparatus is similar in both the wavelength multiplexing systems.

[0040] In general, the wavelength multiplexer of the drop/add type hasthe function of dropping and adding up to M wavelengths relative to thenumber N of multiplexed wavelengths. Here, letter N denotes a naturalnumber, and letter M also denotes a natural number which is equal to orless than the number N. In the wavelength multiplexer shown in FIG. 1,signals demultiplexed into the respective wavelengths of input opticalsignal 7 by the wavelength demultiplexing unit 3 of a specificwavelength dropping section are derived from the specific wavelengthdropping section 2 (first space switching unit 1), and they aredelivered as dropped optical signals outside the apparatus. On the otherhand, optical signals to be added 13 from outside are inputted to aspecific wavelength adding section (second space switching unit 2), fromwhich they are delivered to an output wavelength multiplexing unit 4.Such operations of the wavelength multiplexer are set as dropping,adding and transmitting operations in each node apparatus on the basisof the situation of settings of channels in the whole network.

[0041]FIG. 5 is a schematic block diagram of one embodiment of the nodeapparatus. Signals 39 of respective wavelengths demultiplexed by aninput wavelength demultiplexing unit 33 are first inputted to a specificwavelength dropping unit 31. Subsequently, optical signals 45 ofwavelengths to be outputted as dropped optical signals are derived. Onthe other hand, optical signals to-be-added 44 from outside the nodeapparatus are inputted to a specific wavelength adding unit 32, and theyare multiplexed by an output wavelength multiplexing unit 34. Awavelength converting section 50 for wavelength conversion from inputwavelengths into output wavelengths is interposed between the specificwavelength dropping unit 31 and the specific wavelength adding unit 32.Here, the wavelength converting section 50 has the function ofconverting the wavelengths of optical signals to-be-delivered in amanner to transmit the optical signals from the specific wavelengthdropping unit 31 to the specific wavelength adding unit 32, withoutdropping or adding the optical signals. Thus, the node apparatus in thenetwork architecture shown by way of example in FIG. 4 is permitted toreceive the specific input wavelength signals and to deliver thedifferent output wavelength signals.

[0042] In the node apparatus of this embodiment, except the wavelengthconverting section 50, a wavelength dropping section 51 and a wavelengthadding section 52 input/output signals roughly in the same manner as inthe foregoing node apparatus shown in FIG. 1. More specifically, thewavelength dropping section 51 includes the wavelength demultiplexingunit 33 for input wavelength-multiplexed optical signal 37, the firstswitching unit (or specific wavelength dropping unit) 31 and a filteringunit 35, For example, the wavelength demultiplexing unit 33 and thespecific wavelength dropping unit 31 are connected by an opticalwaveguide, The wavelength demultiplexing unit 33 demultiplexes the inputwavelength-multiplexed optical signal 37 into optical singlans of therespective wavelengths (λ1, λ2, λ3, . . . and λn). The wavelengthdemultiplexing unit 33 suffices with a conventional one. This wavelengthdemultiplexing unit 33 is constructed by employing, for example, afilter formed of a multilayer dielectric film, or a diffraction grating.The respective demultiplexed optical signals 39 are inputted to thespecific wavelength dropping unit 31.

[0043] Optical signals 48 of the wavelengths dropped by the specificwavelength dropping unit 31 are outputted from the node apparatus viathe filtering unit 35. On the other hand, optical singnals 41 of thewavelengths passing through the wavelength dropping unit 31 are inputtedto the wavelength converting section 50. In this wavelength convertingsection 50, the wavelengths which need to be converted are subjected tothe wavelength conversion. Desired passing lights 42 which include thelights of the converted wavelengths, are inputted to the specificwavelength adding unit 32.

[0044] The wavelength adding section 52 includes the second switchingunit (or specific wavelength adding unit) 32, the wavelengthmultiplexing unit 34 for outputting wavelength-multiplexed opticalsignal 38, and a filtering unit 36 for the optical signals to-be-added44. The optical signals 42 transmitted through the wavelength convertingsection 50, and optical signals 46 added via the filtering unit 36 areinputted to the specific wavelength adding unit 32, Lights 40 of theplurality of wavelengths (λ1, λ2, λ3, . . . and λn) outputted from thespecific wavelength adding unit 32 are multiplexed by the wavelengthmultiplexing unit 34. The wavelength-multiplexed optical signal 38 isoutputted from the apparatus,

[0045] Although all the transmitted optical signals are subjected to thewavelength conversion in the embodiment of FIG. 5, only some of thetransmitted optical signals may well be subjected to the wavelengthconversion. Thus, the node apparatus can be made smaller in size,

[0046] Here, the wavelength dropping unit or first space switching unit31, and the wavelength adding unit or second space switching unit 32suffice with conventional members. They are constructed of, for example,optical switches etc. The construction of the wavelength convertingsection 50 may be any of, for example, one which uses electric signalsfor the conversion, and one which uses optical signals for theconversion, First, an example employing electric signals is shown inFIG. 6. The wavelength converting section 50 shown in FIG. 6 includesO/E conversion units 54 (O/E-1, O/E-2, . . . and O/E-N), E/O conversion(E: Electrical, O: Optical) units 56 (E/O-1, E/O-2, . . . and E/O-N),and electrical switching circuits 55 (55-1, 55-2, . . . and 55-N) forindividual wavelengths. The electrical switching circuits 55 areinterposed between the O/E conversion units 54 and the E/O conversionunits 56, and they select output lines of desired wavelengths. Inputoptical signals 1-N (IN-1, IN-2, . . . and IN-N) demultiplexed into therespective wavelengths by the input wavelength demultiplexing unit 33shown in FIG. 5 are respectively converted into electric signals by theO/E conversion units (O/E-1, O/E-2, . . . and O/E-N) 54. As a result,the electric signals numbering N are obtained. Here, each of theelectric signals may be handled as one signal, or it may well bedeserialized into a plurality of low speed signals. All the N electricsignals are inputted to each of the switching circuits 55. Then, apredetermined one of the inputted signals is selected in each of theswitching circuits 55.

[0047] Here, each of the electrical switching circuits 55 is explainedas having the construction of an electrical space switch. However, itcan also be constructed as a time-division switch which switches theinputted electric signals in time-division fashion.

[0048] In FIG. 6, the electrical outputs of the switching circuits 1-Nare respectively inputted to the E/O signal conversion units 56 (E/O-1,E/O-2, . . . and E/O-N). The E/O signal conversion units 56 convert theinputted electric signals from the switching circuits 55 into opticalsignals (OUT-1, OUT-2, . . . and OUT-N) of the respective wavelengths,and output the resulting signals toward the output wavelengthmultiplexing unit 34 shown in FIG. 5, The optical signals OUT-1, OUT-2,. . . and OUT-N correspond to the optical signals of the wavelengths λ1,λ2, λ3, . . . and λn, respectively. By way of example, the switchingcircuit 55-1 is a circuit by which any of the electrical outputs fromthe O/E signal conversion units 54 (O/E units) is outputted to the E/O-1unit among the electrooptic conversion units 56. By way of example, theoptical signal IN-2 (wavelength λ2) is O/E converted by the O/E-2 unit,and the resulting electric signal is outputted to the switching circuits55. This electric signal is delivered to the E/O-1 unit among the E/Oconversion units 56 by the operation of the switching circuit 1 (55-1),and the optical signal OUT-1 of the wavelength λ1 is outputted from theE/O-1 unit. That is, the optical signal IN-2 of the wavelength λ2 iswavelength-converted into the optical signal OUT-1 of the wavelength λ1.The other wavelengths λ2, λ3, . . . and λn can be also converted throughthe switching circuits 55 in like fashion.

[0049] Next, an example in which the wavelength converting section 50 inthe present invention is constructed of optical switches is shown inFIG. 7. In this case, optical signals delivered from the wavelengthdropping section 51 are directly inputted to optical switching circuits57 (57-1, 57-2, . . . and 57-N). Subsequently, one of the opticalsignals is derived by the selecting operation of each of the opticalswitching circuits 57, and it is outputted to the corresponding one ofwavelength conversion units 58 (58-1, 58-2, . . . and 58-N). On thisoccasion, the wavelength conversion units 58 convert the inputtedoptical signals into optical signals corresponding to wavelength Nos.1-N, fixedly irrespective of the wavelengths of the inputted lights.That is, the wavelengths of the lights to be outputted by the wavelengthconversion units 58 are respectively predetermined. Thus, the respectivewavelength conversion units 58 output the optical output signals OUT-1,OUT-2, . . . and OUT-N of the predetermined wavelengths.

[0050] Meanwhile, a technique wherein the wavelengths of outputs can bevariably controlled by a single transmitting optical module has beenproposed, Even with the technique, the wavelength varying functionthereof can be incarnated by employing the wavelength converting sectionof the present invention.

[0051] There will now be described an embodiment of a wavelengthmultiplexer in which routes for all the optical signals of “drop”signals, “add” signals and “through” signals are set by a singleselection unit. FIG. 8 shows an example of construction in the casewhere signals corresponding to all wavelengths are substituted intoelectric signals. A wavelength-multiplexed optical signal 60 isdemultiplexed into individual wavelengths by an input wavelengthdemultiplexing unit 62. The resulting optical signals 63 (wavelengthsλ1, λ2, λ3, . . . and λN) are converted into electric signals by anoptoelectric signal conversion unit (O/E conversion) 64 at thesucceeding stage. Besides, optical signals (adding optical signal) 69 ofpredetermined wavelengths to be added from outside the wavelengthmultiplexer are converted into electric signals by an optoelectricconversion unit (O/E conversion) 68. Here, the electric signals of suchtwo groups are inputted to an electric switching circuit unit 65. In theelectric switching circuit unit 65, both routes for signals 61 to bedelivered to an output wavelength multiplexing unit 70 and for signalsto be delivered (as dropped signals 67) outside the wavelengthmultiplexer can be connected at will by the operations of spaceswitches, The output optical signals 71 to be delivered to thewavelength multiplexing unit 70 are optical signals (wavelengths: λ1,λ2, λ3, . . . and λN) generated in such a way that electric signals fromthe electric switching circuit unit 65 are converted by an electroopticsignal conversion unit 72. The optical signals (wavelengths: λ1, λ2, λ3,. . . and λN) 71 are wavelength-multiplexed by the wavelengthmultiplexing unit 70, and are outputted as output light 61. The droppedsignals 67 are optical signals generated in such a way that electricsignals from the electric switching circuit unit 65 are converted by anelectrooptic signal conversion unit 66.

[0052] Here in FIG. 8, how to connect desired channels is exemplified.The routes of ordinary “drop” and “add” signals are indicated as WSA(Wavelength Slot Assignment). By way of example, symbol WSA (Drop)denotes the dropping channel. Regarding this dropping channel, light ofwavelength λ3 is inputted to the portion 4 of the electrooptic signalconversion unit 66 by the electric switching circuit unit 65 and isconverted into a desired wavelength, which is outputted as the droppedoptical signal 67, The adding channel denoted by symbol WSA (Add) may besimilarly considered. The optical signal to-be-added 69 inputted to theportion 2 of the optoelectric conversion unit 68 is outputted to theportion 3 of the electrooptic conversion unit 72 and is converted intothe optical signal of the wavelength λ3, which is delivered to themultiplexing unit 70. Discrepancy in the ratios between the numbers of“through” channels and the numbers of “drop/add” channels in individualnodes can be adjusted by making it possible to set at will the number(N) of wavelengths to be inputted and the number (M) of signals to bedropped/added. Thus, the range of applications to node apparatuseswidens.

[0053] Here, symbol WSI (Wavelength Slot Interchange) denotes awavelength converting route. In this case, it corresponds to theinstallation of the wavelength converting section according to thepresent invention to secure the wavelength converting route in a spaceswitch. In the example of FIG. 8, input optical signal of wavelength λ1is converted into optical signal of wavelength λ4, which is outputted.

[0054] Further, as shown in FIG. 8, the apparatus of this embodiment canaccommodate an ordinary “through” channel (TR: Through), a connectionchannel (HP; Hairpin) established between an “add” optical signal and a“drop” optical signal, a broadcast type channel (BC: Broadcast) in whichan added optical signal is outputted as a plurality of wavelengthsignals, and so forth.

[0055] Optical signal to-be-added which is inputted to the portion 4 ofthe optoelectric conversion unit 68, is delivered as dropped opticalsignal to the portion 2 of the electrooptic conversion unit 66(Hairpin). Besides, optical signal to-be-added inputted to the portion 2of the optoelectric conversion unit 68 is delivered as branched opticalsignal to the portions 1 (λ1) and 3 (λ3) of the electrooptic conversionunit 66 (Broadcast). Incidentally, the constituents themselves of suchspace switches have been known. They are introduced in, for example,Gerd Keiser “Optical Fiber Communications: Second Edition” published byMcGRAW-HILL Inc., section 11.4 PHOTONIC SWITCHING.

[0056] Network architectures in each of which a plurality of wavelengthmultiplexers according to the present invention are connected, are shownin FIG. 9, FIG. 10 and FIG. 11. An embodiment in FIG. 9 is a networkscheme called “linear network”, in which node apparatuses 81, 82, . . .and 85 are connected in one row. Besides, an embodiment in FIG. 10 is anetwork scheme called “ring network”, in which node apparatuses 91, 92,. . . and 95 are connected in the shape of a ring. Further, anembodiment in FIG. 11 is a so-called “meshed network”. The minimumnetwork unit constructed in the linear network or the ring network istermed a “subnetwork”. In general, the network is constituted by aplurality of subnetworks. An operation system (OPS) 80 or 90 isconnected in common in any of the networks. The OPS has the man-machineinterface of an administrator, and it includes hardware such as aworkstation or a personal computer, various items of supervisory controlsoftware, and means for communications with the node apparatuses.

[0057] Here, the administrator gives the OPS a command concerning achannel which is to be actually opened. It is assumed by way of examplethat a request for adding a channel from the node apparatus A to thenode apparatus D has occurred. Then, the administrator commands the OPSto add the channel. Subsequently, wavelengths to be actually used inindividual zones are selected. Regarding the selection of thewavelengths, the OPS may display the situation of uses of wavelengths onthe screen of a console or the like and prompt the administrator toselect the wavelengths, or the OPS may well select the wavelengthsautonomously under a software control. Here will be explained a methodin which the OPS autonomously selects the wavelengths of the respectivezones in compliance with the channel setting request in the networkincluding the multiplexers of the present invention.

[0058] In each of FIGS. 9, 10 and 11, thick lines indicate the routes ofmain wavelength-multiplexed signals, and dotted lines indicate theroutes of supervisory control signals from the OPS. The supervisorycontrol signals between the respectively adjacent node apparatuses aretransferred by, for example, employing wavelengths different from thoseof the main signal and multiplexing them into a single fiber togetherwith the main signal, Further, in FIG. 9, examples of operations areindicated for the respective node apparatuses 81, 82, 83 and 84.Besides, FIG. 12 is a flow chart for plainly elucidating examples ofoperations in the optical network of the present invention.

[0059] The OPS is always supervising the situation of uses ofwavelengths in subnetworks controlled by itself. It is assumed by way ofexample that a user of the channel has made a request for adding achannel from the node apparatus A to the node apparatus D (100 in FIG.12). Upon receiving the request, the administrator of the channel, forexample, inputs a command to the effect of connecting the above thecircuit channel, from a terminal (for example, personal computer (PC) orworkstation (WS)) (101 in FIG. 12). Then, the OPS searches for thesituation of uses of wavelengths in the node apparatuses A (81), B (82),C (83) and D (84) (102 in FIG. 12). In accordance with the result of thesearch, the OPS determines wavelengths which are to be used between theadjacent node apparatuses (103 in FIG. 12). Subsequently, the OPS givesthe commands of “dropping/adding certain wavelengths” to the nodeapparatuses A (81) and D (84). Further, the OPS gives the commands of“wavelength conversion methods” to the node apparatuses B (82) and C(83) which are midway node apparatuses. Concretely, the OPS transferssupervisory control signals containing commands corresponding to theinstructions, by the communication means (104 in FIG. 12). Theoperations of the node apparatuses responsive to the above operationsare indicated in FIG. 9. That is, each of the nodes A (81) and D (84)executes “Accepting wavelength dropping/adding command” (86 or 89),while each of the nodes B (82) and C (83) executes “Accepting wavelengthconversion method instruction” (87 or 88).

[0060] Each of the node apparatuses A (81), B (82), C (83) and D (84)having received the supervisory control signals judges whether or notthe transferred supervisory control signal is the instruction for itsown node, by checking a node identifier (usually termed “node ID”)affixed to the transferred signal (105 in FIG. 12). In a case where, asa result, the supervisory control signal is the instruction for the nodeapparatus, this node apparatus executes an internal hardware settingoperation complying with the instruction (106 in FIG. 12), and it sendsan executed result back to the OPS (107 in FIG. 12). In a case where thenode ID disagrees with that of the node apparatus, this node apparatusrelays the received control signal to the node apparatus of thesucceeding stage (111 in FIG. 12). More specifically, among theinstructions received by the node A (81), the instructions for the nodesB, C and D bear the affixed node identifiers which disagree with thenode identifier of the node A itself, so that the node apparatus A (81)relays them to the node apparatus B (82) of the succeeding stage.Subsequently, among the instructions received by the node B (82), theinstructions for the nodes C and D bear the affixed node identifierswhich disagree with the node identifier of the node B itself, so thatthe node apparatus B (82) relays them to the node apparatus C (83) ofthe succeeding stage. Thereafter, similar operations are executed in thenode apparatuses C and D. The above operations of the node apparatusesare indicated in FIG. 9. That is, the nodes A (81), B (82) and C (83)execute “Relaying instructions for nodes B, C and D”, “Relayinginstructions for nodes C and D” and “Relaying instruction for node D”(86, 87 and 88), respectively. Besides, the executed result of thehardware setting operation in each node apparatus is sent back to theOPS as “Sending back executed result” (86, 87, 88 or 89).

[0061] After having confirmed the normal terminations of all the nodeapparatuses (108 in FIG. 12), the OPS notifies the results to theoperator or the administrator. Besides, the OPS updates the situation ofuses of wavelengths in the subnetworks (109 in FIG. 12). Thus, theseries of channel opening operations are ended (110 in FIG. 12), and theordinary service of the channel is started. Then, the OPS falls into ausual standby state.

[0062] The operations of the linear network have been explained above byway of example. However, the ring network or the meshed network can alsobe operated in like fashion except alterations based on a differentcircuit arrangement.

[0063] According to the present invention, it is possible to provide awavelength multiplexer which can easily add new channels, and awavelength-multiplexed transmission network which employs suchwavelength multiplexers.

What is claimed is:
 1. An optical multiplex transmission methodcomprising: accepting an optical signal group in which optical signalsof a plurality of wavelengths are multiplexed, from a first opticaltransmission line; converting the optical signal of the first wavelengthincluded in the optical signal group, into the optical signal of thesecond wavelength different from said first wavelength; and multiplexingat least one of the optical signals of the wavelengths except said firstwavelength, included in said optical signal group, and said opticalsignal of said second wavelength, and then outputting the resultingmultiplexed optical signals to a second transmission line.
 2. An opticalmultiplex transmission method comprising: accepting a first opticalsignal group in which optical signals of a plurality of wavelengths aremultiplexed, from a first optical transmission line, and a secondoptical signal group in which optical signals of a plurality ofwavelengths are multiplexed, from a second optical transmission line;converting the optical signal of the first wavelength included in thefirst optical signal group, into the optical signal of the secondwavelength different from said first wavelength; multiplexing at leastone of the optical signals included in said first optical signal group,at least one of the optical signals included in the second opticalsignal group, and said optical signal of said second wavelength, andthen outputting the resulting multiplexed optical signals to a thirdoptical signal line; and multiplexing at least one of the opticalsignals except the optical signals to be outputted to the third opticalsignal line, included in said first optical signal group, and at leastone of the optical signals except said optical signals to be outputtedto said third optical signal line, included in said second opticalsignal group, and then outputting the resulting multiplexed opticalsignals to a fourth optical signal line.
 3. An optical multiplextransmission method comprising: allowing a first node apparatus; toreceive a wavelength-multiplexed optical signal group; to transmit atleast one of optical signals included in the optical signal group, to asecond node apparatus connected with the first node apparatus; toconvert the optical signal of first wavelength included in said opticalsignal group, into the optical signal of second wavelength differentfrom the first wavelength; and to transmit said optical signal of thesecond wavelength to a third node apparatus connected with said firstnode apparatus.
 4. A method wherein a node apparatus multiplexes opticalsignals and transmits the resulting multiplexed optical signals,comprising: receiving a first optical signal group from a first opticaltransmission line, and a second optical signal group from a secondoptical transmission line; optically multiplexing at least one ofoptical signals included in the first optical signal group, and at leastone of optical signals included in the second optical signal group, andthen outputting the resulting multiplexed optical signals to a thirdoptical transmission line; optically multiplexing at least one of theoptical signals included in each of the first and second optical signalgroups, except the optical signals to be outputted to the third opticaltransmission line, and then outputting the resulting multiplexed opticalsignals to a fourth optical transmission line; and converting theoptical signal of first wavelength included in said first optical signalgroup, into the optical signal of second wavelength different from thefirst wavelength, and then transmitting said optical signal of thesecond wavelength to another node apparatus.
 5. An optical transmissionapparatus comprising: an input wavelength demultiplexing unit whichdemultiplexes a first optical signal group including optical signals ofa plurality of wavelengths inputted from a first optical fiber, into theoptical signals of the respective wavelengths; a wavelength multiplexingunit which multiplexes optical signals of a plurality of wavelengths,and which outputs the resulting multiplexed optical signals to a secondoptical fiber; a wavelength dropping unit which externally outputspredetermined optical signals among said optical signals of saidrespective wavelengths demultiplexed by said input wavelengthdemultiplexing unit; a wavelength adding unit which outputs opticalsignals of predetermined wavelength in a second optical signal groupincluding optical signals of a plurality of wavelengths externallyinputted, to said wavelength multiplexing unit; and a wavelengthconverting unit which converts the optical signal of first wavelengthamong said optical signals of said respective wavelengths demultiplexedby said input wavelength demultiplexing unit into the optical signal ofsecond wavelength different from the first wavelength, and which outputssaid optical signal of the second wavelength to said wavelength addingunit.
 6. An optical transmission apparatus comprising: means forderiving at least one optical signal from within an optical signal groupincluding optical signals of a plurality of wavelengths inputted from afirst optical fiber, and for outputting the derived optical signaloutside said optical transmission apparatus; means for converting thewavelength of at least one of the optical signals included in theoptical signal group; and means for outputting said at least one of theoptical signals of the converted wavelength, and at least one of theoptical signals which are included in said optical signal group andwhose wavelengths are not converted, to a second optical fiber.
 7. Anoptical transmission apparatus according to claim 5, wherein saidwavelength converting unit comprises: an optoelectric conversion portionwhich converts said optical signal into an electric signal; a switchingportion which selects a connection route for the electric signal; and anelectrooptic conversion portion which converts said electric signal intoan optical signal of specific wavelength.
 8. An optical transmissionapparatus according to claim 5, wherein said wavelength converting unitincludes: a switching portion which selects a connection route for saidoptical signal; and a specific wavelength conversion portion whichconverts the wavelength of said optical signal into a specificwavelength.
 9. An optical network comprising: a plurality of nodeapparatuses each of which includes the optical multiplexing apparatus asdefined in claim 5, wherein said plurality of node apparatuses areconnected in a scheme selected from the group consisting of one liner, aring shape and a mesh shape.
 10. An optical network according to claim9, further comprising: means for accepting a channel connection requestfor connecting the first and second node apparatuses, and thendetermining wavelength conversion methods in said node apparatusesrelevant to the connection; and means for giving commands of thedetermined conversion methods to the respective node apparatuses.